Ice Ages

The last ice age

Cold environments are usually a result of an ice age. An ice age occurs when the Earth is exposed to cold temperatures over a long period of time. In effect, more snow falls in the winter months and summers start becoming shorter allowing ice sheets and glaciers to expand.

This build up of ice is known as glaciation. An ice age is often referred to as a glacial period; warmer periods are known as interglacial periods. It is thought that the Earth has experienced at least 5 ice ages with the earliest one being traced back to around 2.6 billion years ago. The most recent ice age, known as the Quaternary period, began to develop 2 million years ago which consisted of many periods of glaciation.

The last glaciation period started around 120,000 years ago and covered 1/3 of the Earth, including the majority of Britain. This glacial ice did not begin to melt until 10,000 years ago. The glaciers that formed during this period have calved the land we see today

Earth is currently going through an interglacial period known as the Holocene. Currently 25% of the Earth can be distinguished as a cold environment.

Glaciers

Northcentral Chugach Mountains, Alaska

Glaciers are large masses of ice that form over many years when snow is compressed into ice. Glacial formation is a long, continual process of snow falling in layers which manages to trap air and then compresses. The compact snow is referred to as firn, or sometimes neve. Glaciers are often thought of as being like rivers due to having similar characteristics. Just like a river, a glacier also: - starts in highland areas - flows downhill - has distinctive cross profiles and long profiles - erodes, transports and deposits material. However, glaciers are much more powerful than rivers, eroding the landscape at a much greater scale. Glaciers currently cover around 10% of the Earth’s surface, the majority being in Antarctica and Greenland.

Glacial movement

Glaciers move at a much slower pace than rivers, on average between 7 and 10 km a year.

Glacier movement is usually assisted by melt-water which accumulates at the bottom of a glacier helping the glacier to slide. This results in the middle of glaciers moving quicker than their edges. As a glacier moves, ice is pulled and squashed due to the middle of glaciers moving much quicker than their edges.Melt-water usually forms at the bottom of glaciers which aids their movement.

Tasks

Extension (A level)

There are two types of glacier: Temperate (alpine) glaciers: Temperate glaciers usually survive at melting point and when the summer months arrive, they melt releasing huge amounts of water which can aid the glaciers movement. Temperate glaciers are more likely to erode, transport and deposit material. These glaciers can move by basal flow, extending/compressing flow, creep and surges. Polar glaciers: Polar glaciers are found in areas where temperatures remain below 0°C, for example in the Arctic or Antarctic and therefore no melting will occur. Consequently, polar glaciers move much slower than temperate glaciers as they are frozen to their beds, therefore they are more likely to move by internal flow. These glaciers are less likely to erode, transport and deposit material.

KEY POINTS

Warm based (temperate) glaciers:

- form in low latitude regions

- the basal temperature remains close to the pressure melting point (PMP) resulting in meltwater

- glacial movement is not limited

- basal slippage through regelation slip and creep

Cold based (polar) glaciers:

- form in high latitude regions where there is low relief

- the basal temperature is always below the pressure melting point (PMP), therefore basal sliding is does not occur.

- Glaciers are frozen to their beds, therefore there is little movement, erosion or deposition taking place.